Sebastian Vettel's Malaysian Grand Prix victory was a "wake-up call" for Mercedes, says boss Toto Wolff.
Mercedes dominated the first race of 2015 in Australia after winning 16 of 19 races last year to claim the drivers' and constructors' titles.
However, after Vettel's win for Ferrari, Wolff said: "We didn't expect Ferrari to catch up on the second week.
"So to lose the race fair and square is a surprise and a bit of a wake-up call, which is good for us."
Mercedes were unable to compete with Ferrari in the tropical heat of Sepang because of excessive tyre usage.
"Ferrari deserved to win and from a racing perspective we have to acknowledge they have done great development," Wolff said.
"For F1 it is positive. It is the second race and a second team wins. This is what F1 probably needed.